Scientists from the University of Lancaster had volunteers read excerpts from JK Rowing's "Harry Potter" books while scanning their brains with magnetic resonance imaging (MRI).

The results were clear. Researchers found "significant correlations" between brain activity in regions associated with emotion and certain passages in the books. The passages that sparked brain activity revealed the secret behind Harry Potter's spell: The most emotionally charged passages had the most impact on readers' brain activity.

Here's one emotionally-charged passage, from "Harry Potter and the Goblet Of Fire," the researchers used: "Wormtail screamed, screamed as though every nerve in his body was on fire, the screaming filled Harry's ears as the scar on his forehead seared with pain...."

Passages such as this stimulated the left amygdala region of the brain that is involved in processing emotional reactions, according to the researchers' MRI scans. The more emotionally arousing words a text contained, the bigger the effect that was seen.

Writing in the journal Brain And Language, the scientists said: "When we read a text, specific words reverberate in our minds beyond the more complex message conveyed by the text; the art of choosing the right words with the appropriate affective impact is part of what defines the skill of good writers or speakers."

In other words, compelling writers have the power to "cast spells" on their readers.

That, of course, comes as no surprise to Harry Potter readers around the world long under Rowling's spell.